1. Field of the Invention
The present invention relates to an image fixing device for a copier, printer or similar electrophotographic image forming apparatus. More particularly, the invention is concerned with an image fixing device for applying oil to a fixing roller.
2. Description of the Related Art
Japanese Patent Laid-Open Publication No. 5-27637 discloses an image fixing device as shown in FIG. 10. Referring to FIG. 10, the device includes a fixing roller 101, a pressure roller 102 which is in pressure contact with the fixing roller 101, an oil application roller 103 which is in pressure contact with the fixing roller 101 to apply an offset preventing oil 104, and an oil supply roller 105 which is in pressure contact with the oil application roller 103 to apply the oil. The fixing device has a motor 106 for driving the oil application roller 103 independently of the fixing roller 101. And the motor 106 is controlled to change the rotary speed of the oil application roller 103 according to the copying mode, for example full color mode or mono color mode, so as to keep a constant quantity of oil applied to the fixing roller 101. In that case, the quantity of oil applied to each sheet of transfer paper is about 25 mg.
In that fixing device, however, a motor is necessary to rotate the oil application roller. And the quantity of the oil applied to transfer paper, 25 mg, is too much. Furthermore, judging from the contact position of the oil application roller 103 on the fixing roller 101 and the rotating direction of the rollers 101 and 103, oil is liable to be collected at the nip between the fixing roller 101 and the oil application roller 103 during a standby state. Therefore when the fixing roller 101 rotates, collected oil is adhered to the roller 101, and a patch of oil is formed on the first fed paper.
In another conventional device, the offset preventing oil is directly applied from an oil application felt to the fixing roller, and the quantity of the oil is regulated by a blade contacting the fixing roller. In that device, paper dust and offset toner are accumulated at the contact portion of the felt and the blade. The surface of the fixing roller may therefore be damaged by excessive paper dust and offset toner.